1. Field of the Invention
The invention relates to a display apparatus which is used for a television receiver, a view finder of a video camera, a light bulb of a video projector, a display of a computer, or the like and, more particularly, to an assembly of a driving circuit of such a display apparatus.
2. Related Background Art
As a recent display apparatus, attention is paid to a display apparatus having a display device such as liquid crystal device, plasma light emitting device, electrochromic device, electron emitting device, or the like in place of a CRT.
Each of those display devices has a number of pixels and has an electrode to apply an electric signal to decide an optical state of each pixel.
Further, in order to apply the electric signal to the electrode of the display device, a rigid wiring board called a bus board or a driver board and made of glass epoxy or the like and a flexible wiring board such as a TAB film or the like are used.
Such a structure has been disclosed in U.S. Pat. No. 5,019,201 or U.S. Pat. No. 5,360,943 or the like.
A case where a liquid crystal display panel is used as a display device and a film carrier having a driving IC chip is used as a flexible wiring board will now be described herein.
Hitherto, when connecting the film carrier on which a driving circuit is mounted to a display panel and a bus board, there is a drawback such that outer leads located at both ends among the outer leads on the input side and output side are likely to be damaged by a stress from the outside due to a shock, a vibration, a thermal stress, or the like.
To solve such a drawback, therefore, as shown in FIG. 6, dummy leads 8 and 9 which are electrically not related to the driving for an image display are arranged on both outsides of outer leads 6 and 5 on the input side and output side among the leads of the film carrier, thereby preventing a damage of the outer leads at both ends due to an external stress. In FIG. 6, reference numeral 1 denotes a display panel; 2 a driving circuit such as an IC chip or the like; 3 a bus board; 4 a film carrier; and 7 a soldering land for the dummy leads.
There is a case where a quality of an image which is displayed in a display area is improved by always holding the outside of the display area to display the image to either one of a white state (bright state) and a black state (dark state). Such a method is called frame driving.
FIG. 7 shows an example of a display apparatus. Four electrodes 99 for a frame driving are provided for the display panel 1 and are connected to leads for a frame driving of film carriers 4 and 4xe2x80x2 arranged at both ends of two bus boards 3. Reference numerals 201 and 201xe2x80x2 denote scanning line driving circuits of the film carriers 4 and 4xe2x80x2.
One of methods for the frame driving is a method whereby film carriers and driving circuits of substantially the same construction are used as all of the film carriers 4 and 4xe2x80x2 and all of the driving circuits 201 and 201xe2x80x2 and the apparatus is driven so as to supply a signal for always holding the pixels (frame pixels) on the electrodes 99 for the frame driving in a white or black state to the electrodes 99.
Another method is a method invented by the present inventors namely, a method whereby the structure of the film carriers 4xe2x80x2 at both ends of the bus board 3 is made different from a structure of the other film carriers 4.
FIG. 8 shows a structure of the film carrier 4xe2x80x2 which is used in such another method.
It is also possible to construct in a manner such that an input side and an output side of dummy leads 8xe2x80x2 and 9xe2x80x2 are electrically short-circuited and connected in order to supply a signal for, for example, always displaying in white to the frame driving electrodes 99 on the outside of a display area of the display panel 1, the input side is connected to the bus board 3, and the output side is connected to the terminal of the frame driving electrodes of the display apparatus, thereby directly supplying the signal from the bus board 3 to the display apparatus without passing through the driving circuit 201xe2x80x2 and driving a frame area.
In case of the above structure, the same IC chip as that of another driving circuit 201 can be used as a driving circuit 201xe2x80x2.
There is no need to give a special construction or special driving control for a frame driving to the IC chip.
In case of a structure shown in FIG. 6, since the dummy lead 9 electrically enters a floating state, it functions as a role of an antenna and radiation noises are generated.
To avoid such a problem, when the dummy leads 8 and 9 are short-circuited to the adjacent outer lead 5, the dummy leads 8 and 9 cannot be used for the frame driving of the display panel 1.
In the case where, for example, the dummy leads 8 and 9 are held to a ground and are fixed to a grounding voltage in order to avoid the electrical floating state, a stationary DC voltage difference occurs between the dummy leads 8 and 9 and the outer leads 5 and 6 which are adjacent thereto. At this time, particularly, in a connecting portion between the display panel 1 and the outer lead 9 on the output side, a failure such as disconnection or the like due to an electric corrosion is likely to be caused.
It is an object of the invention to provide a display apparatus without an erroneous operation due to noises.
Another object of the invention is to provide a display apparatus having an assembly of a driving circuit which can also be applied to a display panel which needs a frame driving.
Still another object of the invention is to provide a display apparatus in which disconnection is hardly caused due to an electric corrosion.
Further, another object of the invention is to provide a display apparatus having an assembly of a driving circuit in which a generality is high and costs are low.
The invention is made in consideration of the above circumstances and there are provided a display apparatus comprising a display device, a driving circuit mounted on a film carrier to drive the display device, and a bus board to supply a power source and a signal to the driving circuit and an assembly of a driving circuit of such a display apparatus, wherein a dummy lead is provided along the outside of each of an outer leads on the input side and an outer lead on the output side of the film carrier, and a predetermined voltage is applied to the dummy leads.
In this case, the predetermined voltage value which is applied to the dummy leads is selected to be a value which does not to stationarily apply a DC bias to the voltage of the outer lead on the output side.
One end of the dummy lead is connected to a bus board and the other end is connected to the display apparatus.
According to the invention, by setting the voltage of the dummy lead to a value such as not to apply the DC bias as much as possible for a voltage waveform of the outer lead on the output side, the movement of ions in a connecting portion between the outer lead and the display apparatus can be suppressed and a failure such as a disconnection or the like due to an electric corrosion can be prevented.
Since the dummy lead is not in the electrical floating state, there is no fear of radiation noises from the dummy lead.
On the other hand, since the dummy leads on the input side and the output side are common, by arbitrarily setting the voltage to be applied to a land for the dummy lead on the input side, a voltage can be also directly applied to the display apparatus through the film carrier.